Proton exchange in the nitrate vacuolar transporter AtCLCa is required for growth and nitrogen use efficiency

Abstract

Nitrate is a major nutrient and osmoticum for plants. To deal with its fluctuating availability in soils, plants store it into vacuoles. AtCLCa, a 2NO3-/1H+ exchanger localized on the vacuole ensures this storage process. It belongs to the CLC family that includes exchangers and channels. A mutation in a glutamate residue conserved across CLC exchangers is likely responsible for the conversion of exchangers to channels. Here, we show that a clca mutant of this residue, E203, behaves as an anion channel in its native membrane. To investigate its physiological importance, we introduced the AtCLCaE203A point mutation in a clca KO mutant. We first showed that these AtCLCaE203A mutants display a growth deficit linked to water homeostasis disruption. Additionally, AtCLCaE203A expression is not able to complement the clca defect in nitrate accumulation and favors higher N-assimilation at the vegetative stage. Further analyses at post-flowering stages indicated that AtCLCaE203A results in an increase of N uptake allocation to seeds, leading to a higher nitrogen use efficiency compared to wild-type. Altogether, these results point out the critical function of the AtCLCa exchanger on the vacuole for plant metabolism and development.

Focus on climate change and plant abiotic stress biology

“…In this case, earlier flowering may allow plants to escape some of the detrimental effects of salt stress by completing flowering and seed production before salt-induced damage accumulates. In a similar vein, the work of Hodin et al (2023) provides a molecular illustration of the concept of tradeoffs among stress response, growth, and metabolism. They show that a specific mutation of the tonoplast-localized transporter CLCa converts it from a 2 /1H + exchanger to an anion channel.…”